Fluorescent lamps typically have a transparent glass envelope enclosing a sealed discharge space containing an inert gas and mercury vapor. When subjected to a current provided by electrodes, the mercury ionizes to produce radiation having primary wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the envelope to produce visible light which is emitted through the glass. In some conventional fluorescent lamps, efficient illumination of a white color is provided using a blend of red, green and blue-emitting phosphors.
One of the phosphors commercially used in fluorescent lamps is terbium-doped lanthanum phosphate (LAP), which typically contains 13-15 mole % terbium and about 27-33 mole % cerium. With the rapidly increasing cost of rare earth elements driven by the increasing demand for these materials in various applications and their current limited availability, phosphors with very low RE content that can replace the present rare earth based fluorescent lamp phosphors, such as LAP, are highly desirable.